[LLVMdev] Heads Up: libLLVMCore.a and loadable modules

[Reid Spencer]

The recent change in the library structure to make libLLVMCore.a instead
of LLVMCore.o has caused a little fallout. The problem is LLVM tools
that take a --load option to load a module dynamically may now cause
those modules to fail to load at runtime. This occurs because the tool
with the --load option might not be linking in all of libLLVMCore.a, but
only the object modules actually needed by that tool. Consequently, a
module that uses something not linked into the tool will fail to link at
runtime loading.

For example, Yorion experienced this problem when he wrote a shared
library module that depends on DbgStopPoint which is in
IntrinsicInst.cpp.  His module links fine, but when it is loaded into
"opt" it fails to resolve the DbgStopPoint symbols he uses. That's
because the opt program doesn't use DbgStopPoint and so those symbols
are now missing because opt linked with libLLVMCore.a instead of
LLVMCore.o. 

Simply linking the shared library module with libLLVMCore. a doesn't
help because then you get things like AsmWriterPass being registered
multiple times (once from opt and once from the shared lib being
loaded).

The only solution Yorion and I found was to copy the IntrinsicInst.cpp
code out of lib/VMCore and into his own area where it could be compiled
and linked directly into his module.

There may be other things that are not linked into tools like opt any
more that might cause similar problems for loadable modules. 

I'll file a PR on this.

Reid. 
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